This invention relates to an irrigation system for irrigating land, and is specifically a type generally known as a linear move irrigation system. Such a system is characterized by its movement of the entire conduit over the field. The path of movement may be generally straight or curved, but it is contrasted to the rotating movement of systems commonly known as center pivot irrigation systems where one end of the conduit is anchored at a vertical axis about which the conduit rotates.
There are certain common features with both types of systems. Both have a conduit that extends over a portion of the field to be irrigated which is supported along its length by a series of support towers. Customarily these towers each have drive means associated therewith which, for example, can be electrically or hydraulically operated. Both systems also have a series of sprinklers or other means located along the conduit for dispensing liquid fed through the conduit onto the field, and both have some means for supplying the liquid to the conduit.
There have also been certain advantages and disadvantages associated with both. The problems of controlling the path of movement of a center pivot system are reduced by the fact that one end of the conduit is fixed except for its rotation about a vertical axis. Also, with one end of the conduit anchored, it is relatively easy to supply liquid to the conduit at that point. Such systems are well suited for fields of some configurations, with their suitability being greatly enhanced by recent innovations in corner systems as described and claimed in U.S. Pat. Nos. 3,797,517; 3,802,627; 3,902,668; and 3,979,062.
The linear move irrigation system would have the obvious advantage of being particularly suited for fields with square corners such as rectangular or even curved fields. This is because the pattern of irrigation produced by such a system is generally rectangular as the entire conduit moves in substantial alignment over the field. While this advantage has been apparent, the problem has been to simply, accurately, and reliably control the movement of such a system over the field where, unlike the center pivot system, no portion of the system is linearly fixed.
Proper control is critical. It is critical in maintaining uniform distribution of the liquid over the field, and in maintaining the tower wheels in the same wheel tracks as a linear move system moves back and forth over the field. Otherwise crop damage occurs by excessive mutilation from the wheels. It is also critical to ensure the supply of liquid (water) to the system. One such technique has been a water channel at the side and extending the length of the field to be irrigated. A pump, attached to the end tower of the system with a suitable conduit extending into the channel pumps water out of the channel as the entire system moves down the field. Accuracy of movement is important in order to maintain that conduit within the channel.
Various solutions have been proposed for solving these problems but none are believed by applicant to be entirely satisfactory. For example, one such solution is shown in U.S. Pat. No. 3,613,703 with Stout as the named inventor. In Stout the sensing is done at one end of the irrigation system with support towers at opposite ends of the conduit being controlled such that first one acts as the pivot for the conduit and then the other. As a result, the system moves as a series of alternating arced paths. In Stout, both ends of the system are not made to move at the same speed as the system moves along its defined path.
U.S. Pat. No. 3,974,845 with Indresaeter the named inventor, discloses a control for a linear move system making specific reference to the Stout patent. Unlike Stout, the control of the Indresaeter patent maintains the same speed for the control towers at opposite ends of the irrigation system unless a correction is called for. However, a primary disadvantage of the Indresaeter control is its complexity. The Indresaeter patent teaches the measuring or detecting of both angular and linear displacement of the irrigation system relative to the path of travel. These angular and linear displacements are sensed at a location at the end of the irrigation system. As a result, rather complex circuitry is provided for detecting or measuring these angular and linear displacements, processing the information, and generating signals appropriate for making the necessary corrections.
This invention has solved these problems and overcome the disadvantages of the prior art by providing a linear move irrigation system and control therefor which simply, accurately, and reliably controls the movement of the system over the field along a defined path without the need for complicated measuring and processing circuitry.
This is accomplished in the broad sense by sensing the displacement of a point located forward of the conduit relative to a defined path along which the conduit is to move in mass. It has been found preferable to locate this point and the defined path intermediate the outermost controlled towers and even at a centralized location of the conduit although they can be located at either end of the conduit as well. The movement of support towers near opposite ends of the conduit are automatically controlled in response to sensing a predetermined displacement of the point relative to the path to maintain the point over the path and maintain the wheel tracks of the conduit support towers generally parallel to the defined path. The towers controlled in response to the sensor are preferably located on opposite sides of the path where the path is at an intermediate location.
In a particularly preferred embodiment, the sensor is located at the end of an arm extending forwardly of the conduit and responds to a buried conductor (wire) to which is applied an electrical signal producing an electromagnetic field about the conductor, hence the conductor defining the path of movement over the field. In this embodiment the point is defined by the location of the sensor at the end of the arm and is considered a "real" point. As an alternative, the field coupling of this embodiment can be replaced by an electromechanical coupling where the conductor is replaced by a guide means such as a wire and the sensor has microswitches or the like at the end of the arm that are selectively actuated by contact with the wire when the point or sensor is off the path defined by the wire.
In another embodiment, the forward end of an arm is slidingly connected to a guide means such as a wire which defines the path of travel of the irrigation system. The rear end of the arm is connected to the conduit or its support for pivotal movement about a generally vertical axis. A sensor senses the angular displacement of the arm relative to the conduit from a predetermined angle. In this embodiment the system can also be thought of as sensing the displacement of an "imaginary" point located forward of the fixed relative to the conduit and coinciding with the sliding connection of the arm when the system is on the defined path. The sensor effectively detects when the "imaginary" point is off the path defined by the wire and controls the controlled towers in response thereto in much the same way as with the first embodiment.
This novel control technique has been found to provide extremely reliable, accurate, and exceptionally simple means for controlling the movement of such a system such that the wheels of the support towers stay in their tracks upon back and forth movement of the system over the field to minimize crop mutilation, and further making it possible to use a liquid (water) channel extending the length of the field as a liquid supply to the irrigation system. The result is an extremely uniform irrigation of the field.